A polar bear in a German zoo. Anton's keepers realised something was wrong with him when he started vomiting pieces of fabric. Photograph: Michaela Rehle/Reuters

A polar bear has died after apparently swallowing a jacket or bag dropped into his zoo enclosure by a visitor. The Wilhelma zoo in Stuttgart said on Tuesday that keepers realised something was wrong with the 25-year-old bear, named Anton, when he started vomiting pieces of fabric. He died early on Monday of severe intestinal injuries.

The zoo said it was not clear why Anton ate the object instead of tearing it apart, as he usually did with things that landed in his enclosure. His keepers suspected there was some kind of food inside that the bear was attempting to reach.

The zoo has appealed to visitors to report the loss of large objects, allowing keepers to remove them quickly. It said an elephant seal had died in a previous incident after swallowing a toy animal.